1. Field of the Invention
This invention relates to a catalyst for olefin polymerization and a process for producing the same. More particularly it relates to a catalyst for olefin polymerization, obtained by subjecting a specified Ziegler-Natta highly active catalyst to a preliminary polymerization treatment with a small amount of an .alpha.-olefin and an extremely small amount of carbonyl sulfide, according to which catalyst the reduction in the polymerization activity due to poison impurities contained in .alpha.-olefin used is small and also the percentage of amorphous polymer byproduced is small, and also relates to a process for producing the catalyst.
2. Description of the Prior Art
In recent years, as there have been developed the so-called highly active catalysts i.e. Ziegler-Natta catalysts obtained by combining a catalyst component prepared by reducing TiCl.sub.4 with a specified organoaluminum compound or the like, with an organoaluminum compound, the presence of a trace amount of poison substances to catalyst contained in .alpha.-olefin used has raised a serious problem even in the case of suspension polymerization carried out in an inert solvent.
Among these poison substances to catalyst, particularly carbonyl sulfide (COS), if present in 10 ppm or more in raw material .alpha.-olefins such as propylene, notably. reduces the polymerization activity of highly active catalysts when used in suspension polymerization of propylene. Thus, in such a case, propylene has been purified to remove the catalyst poison substances. On the other hand, it has been known that if carbonyl sulfide is present in a trace amount (e.g. 1.about.10 ppm) in an .alpha.-olefin, the yield of crystalline polymer is improved in the above polymerization using the .alpha.-olefin (Japanese patent application laid-open No. Sho 55-31821/1980).
In view of the foregoing, the present inventors have made extensive research in order to find a catalyst for olefin polymerization which is not only not reduced in the polymerization activity even when exposed to carbonyl sulfide as a poison substance, but also can notably reduce the percentage of amorphous polymer byproduced, contrarily by effectively arranging carbonyl sulfide in the highly active catalyst component. As a result, we have found that in the case where a catalyst obtained by combining a specified, highly active catalyst component with an organoaluminum compound is subjected to a preliminary polymerization treatment with a small amount of an .alpha.-olefin, if an extremely small amount of carbonyl sulfide is used at the same time, it is possible to obtain a catalyst for olefin polymerization having the above-mentioned properties.
As apparent from the foregoing, an object of the present invention (having two aspects) is to provide a highly active catalyst for olefin polymerization, which is resistant to catalyst poisons contained in olefins as polymerization raw material, and according to which the percentage of amorphous polymer formed is small, and a process for producing the same. Another object of the present invention is to provide a process for olefin polymerization using the above catalyst.